Method and apparatus for providing channel quality feedback in an orthogonal frequency division multiplexing communication system

ABSTRACT

In an Orthogonal Frequency Division Multiplexing communication system, a user equipment reports channel quality information that is sufficient to construct a fading profile of a frequency bandwidth and that does not consuming the overhead resulting from the reporting of CQI for every sub-band of the frequency bandwidth. In the communication system, the frequency bandwidth may be represented by multiple sub-band levels, wherein each sub-band level comprises a division of the frequency bandwidth into a number of sub-bands different from the number of sub-bands of the other sub-band levels. The user equipment measures a channel quality associated with each sub-band of a sub-band level of the multiple sub-band levels, selects a sub-band of the sub-band level based on the measured channel qualities, and reports channel quality information associated with the selected sub-band to a radio access network.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from provisional application Ser. No.60/731,976, entitled “METHOD AND APPARATUS FOR PROVIDING CHANNEL QUALITYFEEDBACK IN AN ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING COMMUNICATIONSYSTEM,” and filed Oct. 31, 2005, and is a continuation application ofapplication Ser. No. 11/552,716, entitled “METHOD AND APPARATUS FORPROVIDING CHANNEL QUALITY FEEDBACK IN AN ORTHOGONAL FREQUENCY DIVISIONMULTIPLEXING COMMUNICATION SYSTEM,” and filed Oct. 25, 2006, whichapplications are commonly owned and incorporated herein by reference intheir entirety.

FIELD OF THE INVENTION

The present invention relates generally to Orthogonal Frequency DivisionMultiplexing (OFDM) communication systems, and, in particular, to anexchange of channel quality information in an OFDM communication system.

BACKGROUND OF THE INVENTION

The IEEE (Institute of Electrical and Electronics Engineers) 802.16standards propose using an Orthogonal Frequency Division Multiple Access(OFDMA) for transmission of data over an air interface. OFDMA has alsobeen proposed for use in 3GPP (Third Generation Partnership Project)Evolution communication systems. In an OFDMA communication system, afrequency bandwidth is split into multiple contiguous frequencysub-bands, or subcarriers, that are transmitted simultaneously. A usermay then be assigned one or more of the frequency sub-bands for anexchange of user information, thereby permitting multiple users totransmit simultaneously on the different sub-carriers. Thesesub-carriers are orthogonal to each other, and thus intra-cellinterference is minimized.

In order to maximize bandwidth usage, OFDMA communication systems engagein frequency selective scheduling. That is, for any given TransmissionTime Interval (TTI), the sub-bands may be allocated to users based onmeasured channel conditions. Further, an appropriate modulation schemeand coding scheme may be determined for each sub-band and each TTI basedon the measured channel conditions. The channel condition measurementsare performed by a user equipment (UE), which UE measures channelconditions for each and every sub-band during a measuring period, suchas a Transmission Time Interval (TTI) (also known as a sub-frame) or aradio frame transmission period, and then reports the measured channelconditions for all of the sub-bands to a serving Node B in a ChannelQuality Information (CQI) message. Based on the reported CQIs, an OFDMAcommunication system is able to determine a fading profile of afrequency bandwidth and selectively schedule the sub-bands over ascheduling period, typically one or more TTIs or radio frames, andfurther adaptively determine appropriate modulation and coding schemesfor each sub-band during the scheduling period. However, reporting a CQIfor each and every sub-band may consume a significant amount of uplinksystem overhead, especially for OFDMA systems utilizing a 20 megahertz(MHz) bandwidth and employing as many as 100 sub-bands within thatbandwidth.

Therefore, a need exists for a method and apparatus that provideschannel quality information sufficient to construct a fading profile ofa frequency bandwidth and that does not consuming the overhead resultingfrom the reporting of CQI for every sub-band of the frequency bandwidth.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a wireless communication system inaccordance with an embodiment of the present invention.

FIG. 2 is a block diagram of a user equipment in accordance with anembodiment of the present invention.

FIG. 3 is a block diagram of an exemplary sub-band division schemeemployed by the communication system of FIG. 1 in dividing a frequencybandwidth into one or more sub-bands in accordance with an embodiment ofthe present invention.

FIG. 4 is a block diagram of another exemplary sub-band division schemeemployed by the communication system of FIG. 1 in dividing a frequencybandwidth into one or more sub-bands in accordance with anotherembodiment of the present invention.

FIG. 5, a logic flow diagram of a method for a reporting of informationconcerning sub-band channel quality by a user equipment of FIG. 1 to aserving radio access network of FIG. 1 in accordance with an embodimentof the present invention.

FIG. 6 is a block diagram of an exemplary channel quality message inaccordance with various embodiments of the present invention.

FIG. 7 is a block diagram of an exemplary channel quality message inaccordance with another embodiment of the present invention.

FIG. 8 are graphical representations of an exemplary construction of afading profile for a frequency bandwidth based on level-per-levelchannel quality information in accordance with an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

To address the need for a method and an apparatus that provides channelquality information that is sufficient to construct a fading profile ofa frequency bandwidth and that does not consuming the overhead resultingfrom the reporting of CQI for every sub-band of the frequency bandwidth,an Orthogonal Frequency Division Multiplexing (OFDM) communication isprovided wherein the frequency bandwidth may be represented by multiplesub-band levels and wherein each sub-band level comprises a division ofthe frequency bandwidth into a number of sub-bands different from thenumber of sub-bands of the other sub-band levels. The communicationsystem includes user equipment that measures a channel qualityassociated with each sub-band of a sub-band level of the multiplesub-band levels, selects a sub-band of the sub-band level based on themeasured channel qualities, and reports channel quality informationassociated with the selected sub-band to a radio access network.

Generally, an embodiment of the present invention encompasses a methodfor providing channel quality feedback in an OFDM communication system,wherein a frequency bandwidth may be represented by multiple sub-bandlevels and wherein each sub-band level comprises a division of thefrequency bandwidth into a number of sub-bands different from the numberof sub-bands of the other sub-band levels. The method includes measuringa channel quality associated with each sub-band of a sub-band level ofthe multiple sub-band levels, selecting a sub-band of the multiplesub-band levels based on the measured channel qualities, and reportingchannel quality information associated with the selected sub-band to aradio access network.

Another embodiment of the present invention encompasses a method forproviding channel quality feedback in an OFDM communication system,wherein a frequency bandwidth may be represented by multiple sub-bandlevels, wherein each sub-band level comprises a division of thefrequency bandwidth into a number of sub-bands different from the numberof sub-bands of the other sub-band levels. The method includes selectinga sub-band level, measuring a channel quality associated with eachsub-band of the selected sub-band level, selecting a sub-band of theselected sub-band level based on the measured channel qualities, andreporting channel quality information associated with the selectedsub-band to a radio access network.

Yet another embodiment of the present invention encompasses a method forproviding channel quality feedback in an OFDM communication system,wherein a frequency bandwidth comprises a single sub-band. The methodincludes measuring multiple channel qualities associated with thesub-band, averaging the measured channel qualities to produce an averagechannel quality, and reporting the average channel quality to a radioaccess network.

Still another embodiment of the present invention encompasses a methodfor constructing a fading profile for a frequency bandwidth in an OFDMcommunication system, wherein the frequency bandwidth may be representedby a plurality of sub-band levels, wherein each sub-band level comprisesa division of the frequency bandwidth into a number of sub-bandsdifferent from the number of sub-bands of the other sub-band levels. Themethod includes receiving a plurality of messages that each compriseschannel quality information for a sub-band of a sub-band level of theplurality of sub-band levels and constructing a fading profile for thefrequency bandwidth based on the received messages.

Yet another embodiment of the present invention encompasses a userequipment that is configured to report a channel quality in an OFDMcommunication system, wherein a frequency bandwidth may be representedby multiple sub-band levels and wherein each sub-band level comprises adivision of the frequency bandwidth into a number of sub-bands differentfrom the number of sub-bands of the other sub-band levels. The userequipment comprises a processor that measures a channel qualityassociated with each sub-band of a sub-band level of the multiplesub-band levels, selects a sub-band of the sub-band level based on themeasured channel qualities, and reports channel quality informationassociated with the selected sub-band to a radio access network.

Still another embodiment of the present invention encompasses a userequipment that is configured to report a channel quality in an OFDMcommunication system, wherein a frequency bandwidth may be representedby multiple sub-band levels and wherein each sub-band level comprises adivision of the frequency bandwidth into a number of sub-bands differentfrom the number of sub-bands of the other sub-band levels. The userequipment comprises a processor that selects a sub-band of the pluralityof sub-bands by selecting a sub-band level of the plurality of sub-bandlevels, measures a channel quality associated with each sub-band of theselected sub-band level, selects a sub-band of the selected sub-bandlevel based on the measured channel qualities, and reports channelquality information associated with the selected sub-band to a radioaccess network.

Yet another embodiment of the present invention encompasses a userequipment that is configured to report a channel quality in an OFDMcommunication system, wherein a frequency bandwidth comprises a singlesub-band and wherein the user equipment comprises a processor thatmeasures a plurality of channel qualities associated with the sub-band,averages the measured channel qualities to produce an average channelquality, and reports the average channel quality to a radio accessnetwork.

Still another embodiment of the present invention encompasses a radioaccess network that is configured to construct a fading profile for afrequency bandwidth in an OFDM communication system, wherein thefrequency bandwidth may be represented by a plurality of sub-bandlevels, wherein each sub-band level comprises a division of thefrequency bandwidth into a number of sub-bands different from the numberof sub-bands of the other sub-band levels, and wherein the radio accessnetwork receives a plurality of messages that each comprises channelquality information for a sub-band of a sub-band level of the pluralityof sub-band levels and constructs a fading profile for the frequencybandwidth based on the received messages.

The present invention may be more fully described with reference toFIGS. 1-8. FIG. 1 is a block diagram of a wireless communication system100 in accordance with an embodiment of the present invention.Communication system 100 includes multiple user equipment (UEs) 102, 104(two shown), such as but not limited to a cellular telephone, a radiotelephone, a personal digital assistant (PDA) with radio frequency (RF)capabilities, or a wireless modem that provides RF access to digitalterminal equipment (DTE) such as a laptop computer. Communication system100 further includes a Radio Access Network (RAN) 120 that providescommunication services to each of UEs 102 and 104 via an air interface110. RAN 120 includes a transceiver 122, such as a Node B or a BaseTransceiver Station (BTS), in wireless communication with UE 102 andfurther includes a network controller 128, such as a Radio NetworkController (RNC) or a Base Station Controller (BSC), coupled to thetransceiver. Air interface 110 comprises a downlink 112 and an uplink114. Each of downlink 112 and uplink 114 comprises multiple physicalcommunication channels, including at least one signaling channel and atleast one traffic channel.

Transceiver 122 and controller 128 each includes a respective processor124, 130, such as one or more microprocessors, microcontrollers, digitalsignal processors (DSPs), combinations thereof or such other devicesknown to those having ordinary skill in the art. The particularoperations/functions of processors 124 and 130, and respectively thus oftransceiver 122 and controller 128, are determined by an execution ofsoftware instructions and routines that are stored in a respective atleast one memory device 126, 132 associated with the processor, such asrandom access memory (RAM), dynamic random access memory (DRAM), and/orread only memory (ROM) or equivalents thereof, that store data andprograms that may be executed by the corresponding processor.

FIG. 2 is a block diagram of a user equipment (UE) 200, such as UEs 102and 104, in accordance with an embodiment of the present invention. UE200 includes a processor 202, such as one or more microprocessors,microcontrollers, digital signal processors (DSPs), combinations thereofor such other devices known to those having ordinary skill in the art.The particular operations/functions of processor 202, and respectivelythus of UE 200, is determined by an execution of software instructionsand routines that are stored in a respective at least one memory device204 associated with the processor, such as random access memory (RAM),dynamic random access memory (DRAM), and/or read only memory (ROM) orequivalents thereof, that store data and programs that may be executedby the corresponding processor.

The embodiments of the present invention preferably are implementedwithin UEs 102 and 104, transceiver 122, and controller 128, and moreparticularly with or in software programs and instructions stored in therespective at least one memory device 204, 126, 132 and executed byrespective processors 202, 124, 130. However, one of ordinary skill inthe art realizes that the embodiments of the present inventionalternatively may be implemented in hardware, for example, integratedcircuits (ICs), application specific integrated circuits (ASICs), andthe like, such as ASICs implemented in one or more of UEs 102 and 104,transceiver 122, and controller 128. Based on the present disclosure,one skilled in the art will be readily capable of producing andimplementing such software and/or hardware without undo experimentation.

Communication system 100 comprises a wideband packet data communicationsystem that employs an Orthogonal Frequency Division Multiplexing (OFDM)modulation scheme for transmitting data over air interface 110.Preferably, communication system 100 is an Orthogonal Frequency DivisionMultiple Access (OFDMA) communication system, wherein a frequencybandwidth is split into multiple frequency sub-bands, or subcarriers,that comprise the physical layer channels over which traffic andsignaling channels are transmitted simultaneously. A user may then beassigned one or more of the frequency sub-bands for an exchange of userinformation, thereby permitting multiple users to transmitsimultaneously on the different sub-carriers. Further, communicationsystem 100 preferably operates in accordance with the 3GPP (ThirdGeneration Partnership Project) E-UTRA (Evolutionary UMTS TerrestrialRadio Access) standards, which standards specify wirelesstelecommunications system operating protocols, including radio systemparameters and call processing procedures. However, those who are ofordinary skill in the art realize that communication system 100 mayoperate in accordance with any wireless telecommunication systememploying an Orthogonal Frequency Division Multiplexing (OFDM)modulation scheme, such as a 3GPP2 (Third Generation Partnership Project2) Evolution communication system, for example, a CDMA (Code DivisionMultiple Access) 2000 1XEV-DV communication system, a Wireless LocalArea Network (WLAN) communication system as described by the IEEE(Institute of Electrical and Electronics Engineers) 802.xx standards,for example, the 802.11a/HiperLAN2, 802.11g, or 802.16 standards, or anyof multiple proposed ultrawideband (UWB) communication systems.

In order to selectively schedule the multiple UEs 102, 104 for use ofone or more sub-bands of a frequency bandwidth employed by communicationsystem 100, RAN 120 provides each UE 102, 104 with schedulinginformation for a scheduling period. The scheduling informationtypically includes a reference start time, preferably in units of radioframes such as a starting Cell System Frame Number (SFN) index or astarting Connection Frame Number (CFN) index, a scheduling duration,that is, a duration of a time period during which the providedscheduling information is applicable, for example, in units of radioframes or Transmission Time Intervals (TTIs), and an allocated sub-band.

When selectively scheduling the multiple UEs 102, 104 to use thefrequency bandwidth during a scheduling period, communication system 100may divide the frequency bandwidth into one or more sub-bands at eachlevel. It may be noted that the number of carriers in each sub-bandvaries from level to level. For example, FIG. 3 is a block diagram 300of an exemplary sub-band division scheme employed by communicationsystem 100 in dividing a frequency bandwidth 320 into one or moresub-bands in accordance with an embodiment of the present invention. Asdepicted in block diagram 300, communication system 100 may dividefrequency bandwidth 320 into one, two, four, or eight sub-bands during ascheduling period. Each such division of frequency bandwidth 320comprises a different representation of the same frequency bandwidth andmay be thought of as a different level of division of the frequencybandwidth. As a result, the division of frequency bandwidth 302 into anumber of sub-bands may then be thought of as, and represented by, ahierarchical structure, wherein each increasing level (n) of thehierarchical structure corresponds to a dividing of the frequencybandwidth into a greater number of sub-bands. For example, as depictedin block diagram 300, at a first level (n=0) of the hierarchicalstructure, frequency bandwidth 320 is not subdivided, that is, frequencybandwidth 320 comprises only a single sub-band 301. At a second level(n=1) of the hierarchical structure, frequency bandwidth 320 issubdivided into two sub-bands 302 and 303. At a third level (n=2) of thehierarchical structure, frequency bandwidth 320 is subdivided into foursub-bands 304-307. And at a fourth level (n=3) of the hierarchicalstructure, frequency bandwidth 320 is subdivided into eight sub-bands308-315.

In other words, with respect to the frequency bandwidth depicted in FIG.3, for any given scheduling period, communication system 100 may dividefrequency bandwidth 320 into one, two, four, or eight sub-bands, each ofwhich divisions corresponds to a level (n=0, 1, 2, or 3) of thehierarchical structure. That is, at each level of the hierarchicalstructure (n=0, 1, 2, or 3), frequency bandwidth 320 is divided into‘2^(n)’ sub-bands. A value ‘N’ corresponds to the value associated withthe top level of the hierarchical structure, that is, at the top level,‘n=N,’ (that is, N=3 in FIG. 3) and the number of different levels ofsub-band divisions is then equal to ‘N+1’ (for example, in FIG. 3, thenumber of different levels of sub-band divisions is equal to N+1, or 4).However, one of ordinary skill in the art realizes that a number ofpossible sub-bands per level, and a number of levels of bandwidthdivisions, may vary with the frequency bandwidth employed and is furtherup to a designer of the system, and that the value of ‘N’ may varycorrespondingly. For example, FIG. 4 is a block diagram 400 illustratingan exemplary hierarchical structure of a sub-band division scheme thatmay be employed by communication system 100 in dividing a frequencybandwidth 430 in accordance with another frequency bandwidth divisionscheme. While FIG. 4 again depicts four levels of bandwidth division,the number of sub-bands per level differs from FIG. 3, that is, at leveln=0, frequency bandwidth 430 comprises one sub-band 401, at level n=1,frequency bandwidth 430 comprises three sub-bands 402-404, at level n=2,frequency bandwidth 430 comprises six sub-bands 405-410, and at leveln=3, frequency bandwidth 430 comprises twelve sub-bands 411-422 during ascheduling period.

In order to selectively schedule the multiple UEs 102, 104 to use afrequency bandwidth employed by communication system 100, such asfrequency bandwidths 320 or 430, a UE, such as UE 102, reportsinformation concerning sub-band quality to RAN 120. In the prior art, aUE provides complete channel quality information for all of the toplevel sub-bands, such as sub-bands 308-315 with respect to frequencybandwidth 320 or sub-bands 411-422 with respect to frequency bandwidth430, in each CQI message. However, such reporting may consume asignificant amount of overhead when there are a large number ofsub-bands. In order to conserve system capacity, communication system100 merely requires that UE 102 provide information concerning thechannel quality of a single sub-band, for example, the sub-band with thebest channel quality, rather that providing a channel quality for allsub-bands, during a measuring and reporting period.

Referring now to FIG. 5, a logic flow diagram 500 is provided thatdepicts a reporting of information concerning sub-band channel qualityby a UE, such as UE 102, to a serving RAN, that is, RAN 120, inaccordance with an embodiment of the present invention. Logic flow 500begins (502) when UE 102 measures (504) a channel quality, preferablymeasuring Channel Quality Information (CQI) as is known in the art,associated with at least one sub-band of a frequency bandwidth employedby communication system 100. For example, UE 102 may measure a receivedsignal power, a signal-to-noise ratio, a carrier-to-interference ratio,or a carrier power-to-noise power ratio associated with a signaltransmitted over a channel utilizing the sub-band, or may measure a biterror rate or a frame error rate associated with such a signal. One ofordinary skill in the art realizes that many parameters may be measuredin determining channel quality and that any such parameter may be usedherein without departing from the spirit and scope of the presentinvention.

In one embodiment of the present invention, RAN 120 may inform UE 102 ofthe sub-bands to be measured during a measuring time period. Forexample, RAN 120 may provide UE 102 with a list of frequencies tomonitor during each of one or more measuring periods, or the RAN mayprovide the UE with an identifier, such as an index number, of eachsub-band to be measured during each of one or more measuring periodsand, based upon the identifier, the UE is able to determine thefrequencies to monitor during each measuring period.

In another embodiment of the present invention, UE 102 may bepre-programmed with information concerning which sub-bands to monitorduring a measuring period, which information is also stored at RAN 120,for example, in the at least one memory device 126, 132, of transceiver122 or controller 128. For example, UE 102 may be pre-programmed tocycle through the sub-bands of the frequency bandwidth during successivemeasuring periods. For example, and with reference to FIG. 3, UE 102 maybe programmed to cycle its way through the multiple sub-bands 301-315,one sub-band at a time. That is, UE may measure a channel qualityassociated with only a first sub-band, such as sub-band 301, during afirst measuring period. UE 102 may then measure a channel qualityassociated with a successive sub-band during each successive measuringperiod, such as a channel quality associated with sub-band 302 during asecond measuring period and a channel quality associated with sub-band303 during a third measuring period, working its way through all of thesub-bands and re-measuring a channel quality associated with the firstmeasured sub-band 301 after measuring all of the other sub-bands.

By way of another example, and again with reference to FIG. 3, UE 102may be programmed to cycle its way through the levels (n=0, 1, 2, 3),one level at a time. That is, UE 102 may be programmed to measure achannel quality associated with the sub-bands of level ‘0,’ that is,sub-band 301, during a first measuring period. UE 102 may then measure achannel quality associated with the sub-bands of a next level duringeach successive measuring period, such as a channel quality associatedwith each of the sub-bands of level ‘1,’ that is, sub-bands 302 and 303,during a second measuring period to produce a first multiple measuredchannel qualities, a channel quality associated with the sub-bands oflevel ‘2,’ that is, sub-bands 304-307, during a third measuring periodto produce a second multiple measured channel qualities, and a channelquality associated with the sub-bands of level ‘3,’ that is, sub-bands308-315, during a fourth measuring period to produce a third multiplemeasured channel qualities. After UE 102 measures a channel qualityassociated with the sub-bands of a top level, such as level ‘3’ withrespect to FIG. 3, UE 102 returns to measuring a channel qualityassociated with the sub-bands of the bottom level, that is, level ‘0.’

In still other embodiments of the present invention, UE 102 may measureall of the sub-bands during each measuring period or may measure achannel quality associated with each sub-band of a given level andchannel qualities associated with selected sub-bands of other levels,such as a sub-band of another level whose channel quality was reportedin a previous channel quality message, as is described in greater detailbelow.

In response to measuring the channel quality associated with at leastone sub-band of a frequency bandwidth, UE 102 selects (506) a sub-band,of the at least one measured sub-band, whose channel quality informationis to be reported back to RAN 120 in a channel quality message. When, atstep 506, UE 102 selects a sub-band from among multiple sub-bands whosechannel quality is measured during a measuring period, UE 102 preferablycompares the measured channel qualities to produce a comparison and,based on the comparison, selects a sub-band associated with a bestmeasured channel quality. However, in other embodiments of the presentinvention, UE 102 may, based on the comparison of measured channelqualities, report back channel quality information associated with asub-band that has a middle channel quality of the measured channelqualities or that has a worst channel quality. Multiple algorithms willoccur to one of ordinary skill in the art to be used to determine whichsub-band, of the at least one measured sub-band, whose channel qualityinformation is to be reported back to RAN 120, and any such algorithmmay be used herein without departing from the spirit and scope of thepresent invention. However, the sub-band channel quality informationreported back to RAN 120 should be such that the RAN is able toconstruct, over time, a fading profile for the frequency bandwidthassociated with the sub-bands.

For example, in one embodiment of the invention, UE 102 may reportchannel quality information for the sub-bands on a sub-band-by-sub-bandbasis. That is, during each successive reporting period, UE 102 mayreport channel quality information associated with a successivesub-band. For example, and with reference to FIG. 3, UE 102 may work itsway through the sub-bands 301-315, one sub-band at a time. That is, UEmay report a channel quality associated with a first sub-band, that is,sub-band 301, during a first reporting period, may report a channelquality associated with a next sub-band, that is, sub-band 302, during asecond reporting period, and so on. After reporting a channel qualityassociated with a last sub-band, that is, sub-band 315, UE 102 returnsto the first sub-band, that is, sub-band 301, and reports a newlymeasured channel quality associated with the first sub-band during anext reporting period.

In another embodiment of the invention, UE 102 may report channelquality information for the sub-bands on a level-by-level basis. Thatis, during each successive reporting period, UE 102 selects a next,preferably successive, level and reports channel quality informationassociated with a sub-band of the selected next level. For example, andwith reference to FIG. 3, UE 102 may work its way progressively throughlevels ‘0’ through ‘3,’ one level at a time. That is, UE may report achannel quality associated with a sub-band of a first level, that is,level ‘0’ and sub-band 301, during a first reporting period. During asecond reporting period, UE 102 may report a channel quality associatedwith a sub-band of a next, second level, that is, level ‘1’ andsub-bands 302-303. During a third reporting period, UE 102 may report achannel quality associated with a sub-band of a next, third level, thatis, level ‘2’ and sub-bands 304-307. And during a fourth reportingperiod, UE 102 may report a channel quality associated with a sub-bandof a next, fourth level, that is, level ‘3’ and sub-bands 308-315. Afterreporting a channel quality associated with a top level, that is, level‘3,’ UE 102 returns to the first level, that is, level ‘0’ and sub-band301, and reports a newly measured channel quality associated with asub-band of the first level.

In response to selecting a sub-band whose channel quality measurementsare to be reported back to RAN 120 during the reporting period, UE 102assembles, and conveys (508) to the RAN, during the reporting period, amessage informing of a channel quality, preferably comprising ChannelQuality Information (CQI), associated with the selected sub-band.Preferably, UE 102 includes in the message an identifier of the selectedsub-band along with the associated channel quality information. Forexample, FIG. 6 is a block diagram of an exemplary channel qualitymessage 600 in accordance with various embodiments of the presentinvention. Channel quality message 600 includes a first data field 602that comprises an identifier of the sub-band selected at step 506, suchas an index to one of sub-bands 301-315. Channel quality message 600further includes a second data field 604 that comprises channel qualityinformation, such as channel quality measurements, associated with theselected sub-band.

Channel quality message 600 may further include a third data field 606that comprises an update of channel quality information associated withat least one previously reported sub-band. For example, suppose that afirst data field 602 and a second data field 604 of a current channelquality message comprise an identifier and a channel quality associatedwith a sub-band of level ‘n’ (with respect to block diagram 300, n=0, 1,2, or 3). Further suppose that, in each successive channel qualitymessage, UE is reporting back a channel quality of a sub-band associatedwith a level ‘n’ that is one level higher than the level ‘n−1’ of thesub-band reported in the preceding channel quality message (note that,when the levels are being cycled through in successive channel qualitymessages, after a channel quality of a sub-band of level n=3 is reportedin a channel quality message, the next channel quality message reports achannel quality of a sub-band of level n=0). In such an instance, thirddata field 606 may comprise channel quality information associated withthe sub-band of level ‘n−1’ whose channel quality information wasreported in the preceding channel quality message.

In order to minimize a size of the channel quality message, the channelquality information included in third data field 606 may comprise adifferential value indicating a change in the channel quality of thelevel, or the sub-band that was selected for reporting, whose channelquality information was reported in an immediately preceding channelquality message. Thus RAN 120 knows the level and/or sub-band associatedwith the channel quality information reported in third data field 606without the level or sub-band being expressly identified in the message.For example, if the channel quality information reported for a selectedsub-band in a preceding channel quality message comprises a voltageassociated with a measured channel quality, third data field 606 maycomprise a value associated with a change in such a voltage, such abinary value corresponding to a change in decibels (dBs), resulting froma re-measuring of the sub-band's channel quality during the most recentmeasuring period.

By way of another example and referring now to FIG. 7, a block diagramis depicted of an exemplary channel quality message that comprisesupdates of channel quality information for multiple sub-bands other thanthe selected sub-band. Similar to channel quality message 600, channelquality message 700 includes a first data field 602 that comprises anidentifier of the sub-band selected at step 506 and a second data field604 that comprises channel quality information, such as channel qualitymeasurements, associated with the selected sub-band. Channel qualitymessage 700 further comprises a third data field 702 that includeschannel quality information associated with sub-bands of each ofmultiple levels different from the level of the sub-band being currentlyreported in data fields 602 and 604. For example, suppose the first andsecond data fields 602, 604 comprise an identifier and a channel qualityassociated with a sub-band of level ‘n.’ Third data field 702 may thencomprise multiple data sub-fields, wherein each sub-field reports achannel quality of a sub-band of a level other than level ‘n’ and whichsub-band also is of a level different from the levels of the sub-bandsreported in the other sub-fields. The sub-fields may report sub-bandchannel quality information in a predetermined order, such as a firstsub-field reporting channel quality information for level ‘n+1’ (andpossibly of the sub-band that was the best previous reported sub-bandfor that level), a second sub-field reporting channel qualityinformation for level ‘n+2’ (and, again, possibly of the sub-band thatwas the best previous reported sub-band for that level), and so on, sothat the RAN knows the level and/or sub-band associated with the channelquality information reported in each sub-field without the level orsub-band being expressly identified in the message. Again, in order tominimize a size of the channel quality message, the channel qualityinformation included in each sub-field of third data field 702 maycomprise a single bit associated with a differential value, whichdifferential value identifies a change in the channel quality valuereported for a sub-band or a level associated with the sub-field from avalue that was reported for the sub-band or level in a preceding channelquality message.

When the sub-band being measured comprises the entire frequencybandwidth, such as sub-band 301 with respect to bandwidth 320 orsub-band 401 with respect to bandwidth 430, then the channel qualityinformation reported by the UE may comprise a channel quality valueaveraged over the entire bandwidth. For example, typically channelquality measurements are made for channels that are significantlynarrower than the entire frequency bandwidth. When the frequencybandwidth comprises multiple sub-bands that are each sufficientlynarrow, a channel quality measurement may cover all or nearly all of thesub-band. However, when the frequency bandwidth comprises one or moresub-bands that are particularly wide, such as a single sub-band, such assub-bands 301 and 401, that covers nearly the entire frequencybandwidth, then each sub-band may be associated with multiple channelsthat are measured during a measuring period. In such an event, UE 102may average the channel quality measurements made for the multiplechannels during a measuring period to produce an average channel qualitymeasurement and the channel quality information reported by the UE forthe sub-band may comprise an average channel quality value.

In response to receiving the channel quality message, RAN 120 mayconstruct (510) a fading profile for the frequency bandwidth, such asfrequency bandwidths 320 or 430, and logic flow 500 then ends (512). Forexample, FIG. 8 comprises graphical representations of a construction ofa fading profile for a frequency bandwidth, and in particular frequencybandwidth 430, based on level-per-level channel quality informationprovided in channel quality messages as described herein.

The fading profile for frequency bandwidth 430 that is depicted in FIG.8 may be constructed as follows. A first channel quality messageprovides channel quality information for level ‘0,’ that is, sub-band401. The channel quality information for sub-band 401 is used togenerate bar 801. Another, second channel quality message provideschannel quality information for level ‘1,’ that is, sub-bands 402-404.The channel quality information included in the second message indicatesthat sub-band 404 has a best channel quality of the sub-bands includedin level ‘1.’ This channel quality information, indicating sub-band 404has a best channel quality of the sub-bands included in level ‘1,’ isused to generate bar 802. Yet another, third channel quality messageprovides channel quality information for level ‘2,’ that is, sub-bands405-410. The channel quality information included in the third messageindicates that sub-band 410 has a best channel quality of the sub-bandsincluded in level ‘2.’ This channel quality information, indicatingsub-band 410 has a best channel quality of the sub-bands included inlevel ‘2,’ is used to generate bar 803. Still another, fourth channelquality message provides channel quality information for level ‘3,’ thatis, sub-bands 411-422. The channel quality information included in thefourth message indicates that sub-band 413 has a best channel quality ofthe sub-bands included in level ‘3.’ This channel quality information,indicating sub-band 413 has a best channel quality of the sub-bandsincluded in level ‘3,’ is used to generate bar 804. Thus the bottom bargraph of FIG. 8 is generated, which bar graph provides a profile of thechannel qualities of all of the sub-bands 401-422 of frequency bandwidth430. Based on the bar graph, one of ordinary skill in the art maygenerate the top graph of FIG. 8, which comprises a fading profile ofthe entire bandwidth 430.

Thus by exchanging channel quality messages that each comprises channelquality information associated with a single sub-band, such as singlesub-band of a sub-band level, a fading profile of an entire frequencybandwidth may be constructed. In this manner, communication system 100consumes less overhead in the provision of channel quality feedback thanOFDM systems of the prior art, which prior art systems exchange CQImessages that include CQI for every sub-band of a frequency bandwidth.Further, the channel quality messages fed back by communication system100 may further include updates of channel quality information providedin previous channel quality messages. As these are updates of previouslyprovided information, such as a sub-band whose channel qualityinformation was provided in an immediately preceding channel qualitymessage, a receiving RAN is able to determine the sub-band associatedwith the update without the sub-band being expressly identified in themessage. By not expressly identifying the sub-band in the message,message size may be reduced and system overhead conserved. Further, byincluding updates, such as differential information, rather thancomplete CQI, system overhead is further conserved.

While the present invention has been particularly shown and describedwith reference to particular embodiments thereof, it will be understoodby those skilled in the art that various changes may be made andequivalents substituted for elements thereof without departing from thescope of the invention as set forth in the claims below. Accordingly,the specification and figures are to be regarded in an illustrativerather then a restrictive sense, and all such changes and substitutionsare intended to be included within the scope of the present invention.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any element(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature or element of any or all the claims. As used herein, the terms“comprises,” “comprising,” or any variation thereof, are intended tocover a non-exclusive inclusion, such that a process, method, article,or apparatus that comprises a list of elements does not include onlythose elements but may include other elements not expressly listed orinherent to such process, method, article, or apparatus. Furthermore,unless otherwise indicated herein, the use of relational terms, if any,such as first and second, top and bottom, and the like are used solelyto distinguish one entity or action from another entity or actionwithout necessarily requiring or implying any actual such relationshipor order between such entities or actions.

1. A method for providing channel quality feedback in an OrthogonalFrequency Division Multiplexing communication system, wherein afrequency bandwidth is represented by a plurality of sub-band levels,wherein each sub-band level comprises a division of the frequencybandwidth into a number of sub-bands different from the number ofsub-bands of the other sub-band levels, and wherein the methodcomprises: selecting a sub-band of a first sub-band level of theplurality of sub-band levels based on a predefined list of sub-bands tomonitor; measuring a channel quality associated with one or moresub-bands of a second sub-band level of the plurality of sub-bandlevels, wherein the selected sub-band of the first sub-band level isdivided into a plurality of sub-bands to produce the sub-bands of thesecond sub-band level; selecting a sub-band of the one or more sub-bandsof the second sub-band level; and reporting a channel qualityinformation message for at least the selected sub-band of the secondsub-band level to a radio access network, wherein the channel qualityinformation message comprises channel quality information for eachreported sub-band and an identifier of the selected sub-band of thesecond sub-band level.
 2. The method of claim 1, wherein the firstsub-band level comprises a single sub-band.
 3. A user equipmentconfigured to report a channel quality in an Orthogonal FrequencyDivision Multiplexing communication system, wherein a frequencybandwidth is represented by a plurality of sub-band levels, wherein eachsub-band level comprises a division of the frequency bandwidth into anumber of sub-bands different from the number of sub-bands of the othersub-band levels and wherein the user equipment comprises: a processorconfigured to select a sub-band of the first sub-band level based on apredefined list of sub-bands to monitor; said processor to measure achannel quality associated with one or more sub-bands of a secondsub-band level of the plurality of sub-band levels, wherein the selectedsub-band of the first sub-band level is divided into a plurality ofsub-bands to produce the sub-bands of the second sub-band level; saidprocessor to select a sub-band of the one or more measured sub-bands ofthe second sub-band level; and said processor to report a channelquality information message associated with at least the selectedsub-band of the second sub-band level to a radio access network, whereinthe channel quality information message comprises channel qualityinformation for each reported sub-band and an identifier of the selectedsub-band of the second sub-band level.
 4. The user equipment of claim 3,wherein the first sub-band level comprises a single sub-band.